This proposal is directed towards the development of new approaches to the construction of naturally occurring substances with important biological activity. Three areas of research based on vinylogous amide photochemistry are outlined herein: 1) the extension of the vinylogous amide photocycloaddition/retro-Mannich fragmentation/ring closure sequence to the synthesis of perhydroquinoline ring systems; 2) the application of the photocycloaddition of tertiary vinylogous amides to a construction of the recently discovered manzamine antitumor alkaloids; and 3) a study of the scope and limitations of a novel synthesis of heterocycles based on the photochemistry of vinylogous amides. Taxol (NSC-125973) is an exceptionally promising cancer chemotherapeutic agent with an unusually broad spectrum of potent antileukemic and tumor-inhibiting activity. It is the only plant product known to promote the assembly of microtubules and inhibit the tubulin disassembly process and, thus, appears to be the prototype of a new class of cancer chemotherapeutic agents. Two approaches for the construction of the carbocyclic ring system of the taxane diterpenes are described in this proposal: 1) the application of the intramolecular dioxenone photocycloaddition to the synthesis of taxol analogs and the naturally occurring taxusin; and 2) the development of a highly convergent approach for the synthesis of the taxane diterpenes based on a Grob-like fragmentation of an intramolecular ketene-olefin cycloadduct. The strategies that are outlined herein for the synthesis of biologically active natural products have counterparts in the Diels-Alder reaction, cationic polyene cyclization, and arene-olefin cycloaddition reaction. More than one carbon-carbon bond and considerable stereochemical information is generated in a single synthetic operation. The approaches for the construction of the manzamine alkaloids and the taxane diterpenes outlined in this proposal attest to the considerable potential of this methodology for the synthesis of medicinally important substances.